Parasite Pregnancy

Illustration by Hannah Abraham

SQ FALL INSIDER 2020

Parasite Pregnancy

A POTENTIAL FERTILITY SOLUTION

written by Sharanya Sriram

illustrated by Lu Yue Wang

Grab a glass of drinking water. It’s probably perfectly clear, and if you place it under a microscope, it’s highly unlikely you’ll discover any sort of parasitic worm. Unfortunately, for millions of communities across the globe where access to clean water is scarce, the devastating impacts of parasitic infection trickle into each and every stage of life, including pregnancy. Despite their additional and essential burden of producing and sharing nutrients and antibodies for their baby’s survival, pregnant women are often overlooked in studies regarding the impacts of parasitism on various demographics. However, the few studies which do exist have brought fascinating results: recent evidence has suggested that prenatal parasitic infection can boost fertility, but this attack on the mother’s immune system may result in a compromised fetal immune system.

A study published in Science in 2015 examined the effects of various parasites on lifetime birth average in 986 Bolivian women, where the average was ten children per healthy woman. The researchers found that successive hookworm infections during pregnancy brought the birth average down to seven births per woman, decreasing fertility. A town in Alabama was infected with hookworm as recently as 2017, so Americans may not be as far removed from this issue as we think. In contrast, it was also discovered that roundworm infections during pregnancy were projected to increase fertility, since women infected with roundworms had an average of two more children than healthy women. It turns out that the internal immunological environment caused by roundworm infection is actually similar to one created during pregnancy, leading to an internal state that is more conducive to embryonic implantation in the uterus. In 2018, only 24% of women in the United States who used assisted reproductive technology (such as in vitro fertilization) were able to deliver an infant, so the use of roundworm DNA in fertility treatments may bring promising results for women who have difficulty conceiving.

To determine if parasitic fertility treatments are feasible and ethical, scientists must consider whether prenatal parasitic infection has adverse effects on infant vaccine response. A study published in 2015 did exactly that: researchers examined 450 Kenyan women, of which 79% were afflicted with at least one of the following parasitic diseases: malaria, schistosomiasis, lymphatic filariasis, and intestinal helminths. It’s important to note that the infections were not left untreated over the course of the study; proper treatment was administered during and after pregnancy. After each birth, the newborns were given standard vaccinations for diphtheria (DT), Hepatitis B (Hep B), Haemophilus influenzae (Hib), and tetanus toxoid (TT). For three years after vaccination, the newborns were tested twice a year on their IgG (Immunoglobulin G) antibody levels, which indicated their ability of the children’s immune systems to respond to vaccines. IgG is the most common type of antibody in the body, and it’s also the only antibody a pregnant mother can transfer to her fetus via the placenta, making it an ideal marker for studying the effects of prenatal conditions on fetal immune response.

The researchers discovered that newborns whose mothers had at least one parasitic infection during pregnancy exhibited no statistical difference in lgG levels against two out of four antigens tested (Hep B and TT) compared to healthy mothers. However, when tested for IgG levels against the remaining two antigens (Hib and DT), antibody levels in children of infected mothers were lower than those in children of healthy mothers. Lower IgG levels against Hib and DT indicate inability to produce normal levels of antibodies, leading to higher susceptibility to infection. Unfortunately, this demonstrates that parasitism during pregnancy does impair the child’s ability to respond to vaccinations, emphasizing the need to prevent parasitic infection during pregnancy.

Before determining whether roundworms can realistically be used in fertility treatments, we’ll need a lot more research into the specific effects of roundworm infection on fetal immune response. If such a drug ever enters a clinical trial phase, would it be ethical to purposely inject parasitic DNA into a woman when the infant may suffer detrimental side effects? As immunologists ask these complex questions, we might witness the development of novel fertility solutions within the next few decades. In any case, the complex effects of parasitic infection on pregnancy is a worthwhile topic of study, suggesting that the tools for improving human life often lie within nature itself.

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